1. Field of the Invention
The present invention relates generally to defect judgement methods of industrial products at the production processes and, more particularly, is directed to a defect judgement method for industrial products in its production line that utilizes a video camera and a computer or the like.
2. Description of the Prior Art
Defect detection methods are conventionally practiced in which a light is irradiated on an inspected object, a video camera picks up the image of the inspected object based on its passed or reflected light, and the image signal from the video camera is processed by an electronic processor such as a computer or the like which makes the judgement of the object.
Further, upon making the judgement as to whether the defect should be detected or not, methods involving means that a certain threshold value is setup against the image signal and that such a portion that responds to an image signal that exceeds the above threshold value is judged as a defect, have been mainly employed.
Generally, the shape of the flaws or the like that are to be detected as defects are extensively varied, for instance, some that contain severe notches or unevenness at the circumference, or a grouping of multiple small variant portions that look like a single flaw, etc. Accordingly, by the defect judgement methods that are conventionally practiced by setting up a mere threshold value against the image signal to judge anything exceeding such value as a defect, it is extremely difficult to determine the judgement basis as whether it should be a defect or not against flaws that contain such shape variations. For instance, a flaw that contains at its central portion a narrow crevice that visually appears as two flaws on micrographic basis shall be judged as one flaw by the conventional methods to an extent that an accurate judgement of defects was impossible.